Concrete continues to gain in popularity as a building material of choice in flooring applications due to its structural integrity, wear resistance and cost economy. With this growing use, the varying tastes of the public desire improved aesthetics similar to those available in other attractive floorings such as terrazzo or ceramic tile. Those floorings are much more expensive than concrete and do not offer the structural advantages of. continuous concrete paving.
Recently, surface seeded exposed aggregate concrete has come to favor, in which subsequent to the pouring of the concrete, a mass of hard inert materials such as sand or gravel is broadcasted, i.e., seeded, over the top surface of the concrete and subsequently troweled into that surface. Upon curing, the aggregates adheres to the concrete surface and are thus exposed. When first introduced, the surface seeded exposed aggregate technique normally required aggregates approximately three-eighths of an inch diameter mean size or greater to provide sufficient ability to adhere to the concrete upper cement surface, resulting in a rough surface that limited widespread use of the technique in flooring applications.
Applicant recognized this deficiency and developed a method to effectively reduce the size of the aggregate exposed on the surface of the concrete, as disclosed in U.S. Pat. No. 4,748,788 (issued Jun. 7, 1988) and hereby incorporated by reference in its entirety. In that prior invention, Applicant developed a method for producing a decorative slab by pouring a concrete mixture over a prepared subgrade, finishing the upper surface of the mixture with a bull float, spreading a layer of aggregates less than 3/8 inch diameter over the mixture and mixing the two together, applying a chemical retarder and washing and curing the mixture. The resulting exposed aggregate concrete surface provided aesthetics and wear resistance similar to flooring such as granite, marble or stone.
Applicant now aims to expand the colors and surface texture appearances of concrete surfaces which may be produced by the methodology of the surface seeded exposed aggregate technique of the prior invention. One limitation on the variety of surfaces producible has been the perceived non-compatibility of placing certain materials in the concrete mixture, in that scientists have reported of chemical reactions occurring over time degrading the surface. See e.g., McConnell et al. "Cement-Aggregate Reaction in Concrete," J. An. Concrete Inst., Vll. 19, No. 2, Pg. 93 (1947). Silicious materials found in concrete aggregate are well known to react with alkalies in Portland cement, creating silicious gels which lead to expansion, cracking and exudations upon exposed surfaces, though specifications now typically limit alkali content in cement to 0.6% to inhibit such subsequent reactions in concrete aggregates. Minerals other than silicates found in concrete aggregate appear to react only to an insignificant extent, and are usually deemed innocuous.
The relationship of the reactivity of particulates in concrete to numerous factors is recognized as complex. For example, expansion resulting from reaction between aggregates and cement alkalis is believed increased with increases in cement content, due to the greater abundance of available alkalies. For reactive aggregates, maximum expansion of concrete tends to increase as the particulate size of the reactive material decreases. Experience further indicates that the expansion of deleterious aggregate and high-alkali cement may be lower if the aggregate is porous. In addition, some materials may be deleterious for reasons other than reactivity with alkalis released during hydration of cement; for example, sulphates have been known to react with silicates of cement.
No single hypothesis is known to explain quantitatively the variations in degradation of concrete with changes in the makeup of the concrete. Applicant desires to place a variety of potentially reactive particulates of a small diameter into the upper cement surface of concrete flooring. As such, a method of precluding the effects of the potential chemical reactions between desired exposed materials in the concrete mixture must be developed to allow usage of the desired exposed material.